The present invention relates to a gas pressure gage for measuring a pressure in a vessel such as a vacuum chamber.
A diaphragm pressure gage based on a system of utilizing a pressure difference applied on a diaphragm of an elastic material, a Pirani gage utilizing thermal conduction, an ionization-type pressure gage based on a system wherein a gas is ionized by electrons and an ion current generated thereby is measured so as to measure an amount proportional to the molecular density of the gas, etc. have been known heretofore as the gas pressure gages for measuring gas pressure in a vacuum chamber of a semiconductor element manufacturing apparatus, or the like.
A unitary gas pressure gage enabling the measurement of pressure in a wide range from an exhausting process of a pump to an achievable pressure (10.sup.-10 .about.10.sup.-6 Torr) and an operating pressure (10.sup.-3 .about.10.sup.-1 Torr) is demanded in regard to apparatuses, including the semiconductor element manufacturing apparatus, which utilize vacuum.
The diaphragm pressure gage and the Pirani vacuum gage used heretofore can not be employed solely, however, since a region measurable therein by a single measuring element is of so low vacuum as the atmospheric pressure to 10.sup.-3 Torr. The conventional ionization-type vacuum gage can not be employed solely either, since a region measurable therein by a single measuring element is of so high vacuum as 10.sup.-3 .about.10.sup.-10 Torr, to the contrary.
In order to measure the whole of these regions (from the atmospheric pressure to 10.sup.-10 Torr), therefore, it is necessary to mount at least two kinds of gas pressure gages for different measuring regions on separate flanges and to fit these flanges to a chamber, which would be troublesome and inconvenient. It is impossible practically, on the other hand, to incorporate the diaphragm pressure gage or the Pirani vacuum gage and the ionization-type vacuum gage integrally into one flange to form a single gas pressure gage, since the structure of a pressurereceiving element becomes large in size.